The present invention generally relates to optical pick-up devices assembled in an optical disk apparatus, and more particularly to a structure for supporting a mirror such that a laser beam is reflected by the mirror towards an objective lens.
On a part of a mirror of an optical pick-up device, there is provided a mechanism for a fine adjustment of inclination angle such that the laser beam is directed to the objective lens properly. When a distortion is developed on a reflection surface of the mirror in such a device, the beam spot on a disk is distorted and the playback of information is deteriorated. Thus, there should be no distortion occurring on the reflection surface of the mirror. For this reason, the said mechanism of fine adjustment of the inclination angle has to be able to perform fine adjustment of the inclination angle without causing distortion on the reflection surface.
It should be noted that the mirror is located close to an actuator used for focusing and tends to be subjected to vibration when the actuator is operated. If the said adjustment mechanism is attempted to be structured to meet the above requirement, it is necessary to design the part for supporting the mirror to have a smaller diameter. The part in this case, however, receives vibration from the actuator and becomes more susceptible to cause resonance. When a resonance is developed, the focus or tracking servo control system causes oscillation, leading to loss of focusing or tracking control. Therefore, the said adjustment mechanism needs to be structured so as to suppress the vibration of the mirror. In other words, the structure of the part for supporting the mirror is required: (a) to be able to perform fine adjustments of the inclination angle without causing a distortion on the reflection face; and (b) to be able to suppress the vibration of the mirror.
In a conventional mechanism as will be described in detail later, a table structure comprising a first table part and a second table part coupled each other at their center by a boss of a small diameter is mounted to the main body of an optical pick-up device, and the fixed mirror is mounted on the first table part located at the upper side. When the inclination of the fixed mirror is adjusted in such a mechanism, the second table which is located at the lower side is pushed by means of adjustment screw and is inclined. When the second table part is inclined, the first table part is inclined responsive thereto. Thus, the inclination of the mirror is adjusted. It should be noted that the first table part is inclined while maintaining its flatness, and the mirror is adjusted of its inclination angle without causing distortion on the reflection surface.
In such a pick-up device in which the first table part is coupled to the second table part only by a boss of small diameter, however, there is a problem in that it easily picks up vibration and the mirror vibrates together with the first table part. Vibration of the fixed mirror gives an adverse effect, especially to the tracking servo operation as it causes abnomal reproduction of the information.